I’ll just toss in a real world example of how military and civil aviation might share airspace near a conflict zone.
Granted every country has it’s own procedures but i’m’ currently flying commercially in a country that is at war with it’s southern neighbor. There is the border between the two countries that we don’t cross, unless armed to the teeth and then there is a border that’s pushed further to the north say 150 NM or so which has some altitude restrictions.
Within this border all airspace from FL270 and above is military and below civilian (sometimes the military airspace will allow civilian traffic depending on military activity). This allows the airlines to fly (uncomfortably) below the military airspace to as close as 17 NM to the border.
Military aircraft will depart climb out with Departure Control, and then handed off to Tactical (AWACS) who is in charge within that airspace from 270 and above. Center Controllers only have the space below 270 within the boundaries of this special use airspace. So civil aviation is out of the way completely near the FEBA.
I was on the ground during one occasion when our airport was attacked and had just missed being a casualty by 2 minutes after looking back. To say the least its a bit unnerving. Anyway thought I would share something current that might give you some insight on this original post.
Cheers
One other thing is were issued Air Defense Codes in case queried by a Fighter or AWACS. I know some guys who were in the air near the airport as Patriots were flying over their heads shooting down inbound missiles ooooooffff.